Certain types of fire extinguishers, such as the CO.sub.2 type, are provided with an operating handle which is maintained in the closed position by a spring. Unintentional operation of the device is prevented by a pin extending through apertures in the handle and the handle support. The pin is wired in place by a seal of the so-called "lead and wire" type. The wire, which is easily broken, is imbedded in a lead pellet to give evidence of tampering or use. The assembly of the components of such a device is time-consuming and expensive. The use of a metal pin also has other disadvantages, in that the fire extinguisher is frequently required to be used by persons not familiar with the locking means, who try to depress the operating handle without removing the pin. Under the conditions of stress usually prevailing when a fire extinguisher is needed, the user, in applying excessive force to the handle, often bends the pin so that it is unsuitable for re-use, and in some cases the force applied has been so great that the pin has been jammed between the operating handle and the handle support, rendering the extinguisher inoperative, and so deforming the pin that it could not be removed by hand.